The present invention relates to ball valves and more particularly to ball valve seat and seal designs using materials and configurations that increase the temperature and pressure performance of the ball valve.
Ball valves are well known to those skilled in the art. One design that has met with substantial commercial success is the 60 Series ball valve manufactured and sold by Swagelok Company and as described in U.S. Pat. No. 4,410,165 (hereinafter the xe2x80x9c""165 patentxe2x80x9d) and U.S. Pat. No. 4,602,762 the entire disclosures of which are fully incorporated herein by reference. This ball valve design is characterized by a number of features that improve the seal performance and cycle life of the valve. The valve includes a pair of seat assemblies each on an opposite side of the ball member. Each seat assembly includes a flexible seat ring, a support ring and a disc spring. The disc spring urges the seat ring into sealing engagement with an outer surface of the ball, and the support ring reduces inward axial displacement and deforming of the seat ring when the valve is under pressure. A significant feature of the ball valve is that the ball and seats are xe2x80x9cfloatingxe2x80x9d in that the ball can shift axially under pressure. The floating ball design avoids the need for trunnion style mounting or other costly alternatives.
In accordance with one embodiment of the invention, a ball valve includes a body having a passageway extending therethrough and a ball member disposed in the passageway and mounted for selective rotation between valve open and valve closed positions to control fluid flow through the valve. The valve body includes a pair of annular flange grooves on opposite sides of the ball, with each flange groove extending radially from the passageway. A pair of seat rings are disposed in the passageway on opposite sides of said ball. Each seat ring has a first sealing surface in contact with an outer surface of the ball and a radially extending annular flange or tab received in an associated one of the flange grooves. Each seat ring is spring loaded in the axial direction by a respective disc spring to load the first sealing surface against the ball. In accordance with one aspect of the invention, the seat peripheral flanges are held firmly in place such that the first sealing surface exhibits a cantilever type movement when the valve is under pressure. This prevents excessive axial displacement of the seat under pressure, and also allows the energized load applied to the seats to effectively re-seat the first sealing surface against the ball when the pressure returns to a lower value.
In accordance with another aspect of the invention, each seat ring is provided with the radially extending flange or tab that is axially compressed within a flange groove. The seat flange is configured to resist fluid pressure from two different directions, especially when the valve is under pressure and subjected to elevated temperature cycles. In a first embodiment, each seat flange is axially loaded by the resilient disc spring and by an energized resilient seal having spring-like characteristics disposed in the flange groove. The energized flange seal is used to provide a body seal and to maintain the body seal even after temperature cycling. The resilient flange seal may be fairly stiff such as a flexible graphite seal or a less stiff seal such as an elastomeric seal. The resilient flange seal is used primarily as a body seal. In an alternative embodiment, the disc spring may be omitted with the energized flange seal being used to apply a sufficient active load on the seat flange.
In accordance with another aspect of the invention, a ball valve seat ring is provided of PEEK or other relatively harder and stiffer plastic material compared to PTFE to increase the temperature and pressure performance of the valve.